1. Field of the Invention
This application relates to the delivery of acoustically corrected playback of recorded audio in an enclosure like a car, living room, studio, hall, or any environment where the audio is played through speakers or earphones.
2. Background of the Invention
When an audio recording takes place it is usually a staged venue, either in a studio, live event which could be in a small club, concert stage or an auditorium, and usually has a recording engineer running an audio mixing device with a number of microphones and line inputs to enhance the audio recording. One of the more important aspects of the recording is the enclosure where the recording takes place is what is termed “an acoustic environment.” In many cases, such as a large concert hall, the enclosure has been acoustically designed to enhance the listening experience for the audience. We have all listened to a symphony played by a large orchestra in a hall where the acoustics are designed to enhance the music and marveled at the sound. Yet if we have a recording of the exact piece, when we play it at home or in the car the sound lacks the presence we remember.
The quality of the sound is also affected by the electrical components used to reproduce it. For example the amplifier through which the recording is played will alter the sound by amplifying, cutting, or delaying certain aspects of the original signal due to the amplifier's inherent frequency response. Also proper speakers are needed with enough range to cover the audible frequency range (20 Hz to 20 KHz). Placement of the speaker or speakers is also important to balance the sound arriving to the ear. However, this will not correct the deficiencies inasmuch as enclosure acoustics will still affect the sound delivery to the ear.
There are devices, practices, and systems that allow amplifiers to play audio in an environment, which has been corrected dynamically by modifying the speaker and amplifier response using active filters. These modifications to the playback sound fit the acoustics of the enclosure so as to allow the ear to receive audio as a flat response without reflective variances of the sound waves. The devices, practices and systems mentioned are well known to the current audio recording industry.
As television systems have evolved to offer high definition, so too has the quality of the sound accompanying the video program. At the time the transmission system transitioned to ATSC (Advanced Television Standards Committee) the audio playback system also changed from stereo to AC3, which was invented by Dolby™ and is referred to as Dolby Digital™. This audio system offers 5.1 channels of digital compressed audio as part of the MPEG 2 digital transmission standard for terrestrial broadcast, which is also a compressed format.
Because of these and other changes, analog audio has effectively changed to a digital scheme called AES/EBU (Audio Engineering Society/European Broadcast Union). This standard incorporated in Europe originally was adopted in the US so as to enhance facilities' audio transmission and routing in mixing and distribution of the audio signals for television, radio and other programs. Digital audio offers many advantages over analog audio including dynamic range of over 100 dB or better (based on the bit size and sample rate of the AES signal) and the ability to transmit the signal over long copper cables or even further via fiber optic networks due to it being a serial data scheme. Also one can transmit two audio channels together because of the structure of the AES signal. There are many different styles of the AES standard but this application concerns itself principally with AES 3.
Film production is another venue where acoustical information during audio production is important. When film is shot on location and acoustics outside are uncontrollable, mixing for a film audio is typically done on a sound stage by watching the content or action and performing what is called “mix to pix.” Also sweetening (adding or refining sound content) is performed on the audio production. The studio enclosure where this action occurs may be acoustically balanced to allow the sound mixer to hear the sound clearly without room acoustic impulses. These production techniques are used to enhance the viewer's listening experience and overcome any deficiencies of the playback audio system, including acoustic impairments brought on by scene changes from indoors to outdoors. These practices also apply to television productions.
The present application takes advantage of the technology changes brought on by digital audio, the progression of electronic integrated circuits, the transmission standard known as AES 3, and the production complexities of modern entertainment to provide a system that allows such audio equipment to duplicate the acoustical information of the original recording. This functionality can advantageously be added to electronic equipment consisting of an amplifier and speakers to change the acoustic dynamics of the playback room with or without an active system designed to enhance the room's response to the sound waves.